The invention relates to a semiconductor device. More specifically, the invention relates to a method for forming a capacitor in a semiconductor device capable of exhibiting a high capacitance and a low leakage current.
Recent trends toward highly integrated semiconductor devices have brought about a reduction in cell size thereof. As a result, it is increasingly difficult to form capacitors that have a sufficient capacitance (Cs). In particular, a principal factor in obtaining highly integrated dynamic random access memories (DRAMs) consisting of a transistor and a capacitor is minimizing the area of the capacitor (which occupies a large amount of space in a chip) while maximizing the capacitance of the capacitor. To obtain the capacitance required for each unit cell, there have been actively developed dielectric materials having a high dielectric constant (k). With a decreasing design rule, there has been an increased demand to obtain the required capacitance.
Various methods have been suggested to obtain the desired capacitance. First, a high dielectric material, such as hafnium oxide (HfO2), alumina (Al2O3), or a multi-layer laminate of these materials is used to form a capacitor dielectric layer. When the high dielectric material is used for the capacitor dielectric layer, atomic layer deposition (ALD), rather than chemical vapor deposition (CVD), is performed based on the large aspect ratio of the capacitor.
Second, there is suggested a structure of metal/insulator/metal (MIM) in which upper and lower electrodes in a capacitor are made of metallic materials having a large work function as a method for imparting superior dielectric performance to the dielectric layer to secure a desired capacitance.
In such a MIM structure, a titanium nitride (TiN) layer is widely used as the electrode material of the capacitor owing to its simple formation process. The titanium nitride (TiN) layer is formed with a mixed gas of titanium tetrachloride (TiCl4) and ammonia (NH3). Chlorine (Cl), generated as a by-product upon the formation of the titanium nitride (TiN) layer, exists in the layer. The residual chlorine (Cl) remaining in the layer causes problems, including a significant increase in specific resistance and thus an increase in contact resistance.
To remove the chlorine (Cl) from the titanium nitride (TiN) layer and improve the qualities of the layer, high-temperature annealing is performed under a nitrogen or ammonia atmosphere after deposition of the titanium nitride layer.
However, in a case where a dielectric layer of the capacitor is made of a material having a high dielectric constant, the dielectric layer has a degraded thermal stability, thus making it incapable of withstanding the thermal stress of subsequent heating processes. That is to say, the dielectric layer undergoes excessive or abnormal crystallization upon the subsequent high-temperature process, thus inducing the formation of a grain boundary. The grain boundary causes an increase in leakage current, thus making it impossible to utilize the dielectric layer in the capacitor. When an electrode is made of titanium nitride, the subsequent heat-treatment cannot be performed under a high temperature. As a result, chlorine (Cl) remains on the electrode, thus causing a deterioration in the conductivity thereof. In addition, chlorine (Cl) accumulates at the interface between the electrode and dielectric layer, and a trap site is formed on the interface therebetween, thereby disadvantageously causing an increase in leakage current of the capacitor.